In order to enhance descaling performance, there has been a demand in recent years for the above-mentioned descaling nozzle to jet ultrahigh-pressure water with a pressure of about 30 to 100 MPa. However, the higher pressure of such ultrahigh-pressure water wears orifice peripheries of the nozzle body at the greater rate through contact with the orifice peripheries. In order to meet the demand, it is necessary to minimize the wear of the orifice peripheries, thereby to increase durability.
When the jetting high-pressure water is collected for repeated use, the high-pressure water contains fine scales and the like. The fine scales and the like further accelerate the wear.
Under the circumstances, it has been considered to increase the hardness of the cemented carbide forming the nozzle body, thereby to improve wear resistance of orifice peripheries. For example, the nozzle body may be formed of a carbide hard metal containing tungsten (W) as its main component. However, it is known that, with increased hardness, tenacity and impact resistance are impaired to become susceptible to chipping (Japanese Laid-open Patent Application No. 4-348873).
In a conventional descaling nozzle, as shown in FIGS. 12-14, a nozzle tip 01 acting as a nozzle body includes a groove 03 of U-shaped cross section formed in a distal end thereof and crossing a high-pressure water discharge passage 02 in a downstream position with respect to a high-pressure water jetting direction. An elongated (when seen in the high-pressure water jetting direction) orifice 04 is formed at the intersection of the high-pressure water discharge passage 02 and the groove 03. Orifice peripheries 05 define thin wall portions 06 in the form of knife edges in bottoms of the groove 03 and at longitudinal positions of the orifice (Japanese Laid-open Patent Application No. 1-111464).
When ultrahigh-pressure water is jetted with a higher pressure than before, the thin wall portions 06 tend to be worn away or chipped as indicated by dot-and-dash lines in FIG. 13. The orifice peripheries 05 are damaged quickly, resulting in a deformation of the orifice 04 and a reduction in the jetting pressure of the ultrahigh-pressure water to become unable to remove scales efficiently. Thus, there is a drawback that the durability of the orifice peripheries 05 cannot be improved. Particularly where ultrahigh-pressure water containing fine scales is jetted, there occurs a drawback that the thin wall portions 06 are more susceptible to chipping due to the fine scales colliding with the thin wall portions 06.
When descaling rolled metal, a plurality of descaling nozzles are often juxtaposed for use. Ultrahigh-pressure water jetting from one descaling nozzle may splash in the longitudinal direction of the groove 03 of another descaling nozzle and collide with the thin wall portions 06 of that nozzle tip 01. This may also result in early damage of the orifice peripheries 05.
The present invention has been devised to solve these drawbacks of the prior art, and its object is to provide a descaling nozzle which includes orifice peripheries of improved configuration whereby the orifice peripheries have increased wear resistance against ultrahigh-pressure water, and which effectively prevents the orifice peripheries from being damaged due to a decrease in the impact resistance resulting from the increased wear resistance.